


Sharp

by Cornflower_Corvid



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Anal Fingering, Anal Sex, Danger Kink, Drug-Induced Sex, Established Relationship, Excessive Come, FE3H Monsterfucking Weekend 2020, Fire Emblem: Three Houses Golden Deer Route Spoilers, I'm not going to deny it, M/M, Male My Unit | Byleth, Mild Blood, Minor Violence, Multiple Orgasms, Non-Consensual Drug Use, Overstimulation, Plot What Plot/Porn Without Plot, Post-Coital Cuddling, Prostate Milking, References to Drugs, Rimming, Rough Sex, Scent Kink, Size Kink, Sort Of, Spoilers, Transformation, but the plot is there to make the porn happen, monster cock, partially draconic transformation, there is actually sort of a plot
Language: English
Status: Completed
Published: 2020-11-06
Updated: 2020-11-06
Packaged: 2021-03-08 21:33:46
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 8,396
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27423526
Author URL: https://archiveofourown.org/users/Cornflower_Corvid/pseuds/Cornflower_Corvid
Summary: {War Phase} Byleth is experiencing a ferocious irritability the day after drinking part of a bottle of mead that was gifted to him by an unknown merchant. He locks himself in his room so he doesn't risk harming anyone, but he knows that eventually someone will come looking for him. Claude tries to convince him to see Manuela or one of the other healers, but he refuses, unwilling to give Claude the full truth as to why. Claude tells Byleth that he will just tell Yuri, and at the mention of his partner, Byleth becomes filled with a desire to lay claim to him.
Relationships: Yuris Leclair | Yuri Leclerc/My Unit | Byleth
Comments: 2
Kudos: 66
Collections: FE3H Monsterfucking Weekend 2020





	Sharp

**Author's Note:**

> This was written for the FE3H Monsterfucking Weekend event on twitter, though I finished it late.
> 
> I'm going to put some background summary type stuff in the end notes just to make it a little clearer what's going on here.

“Byleth?”

Byleth looked up quickly, not realizing how hard he was concentrating on forcing himself to stay calm. How long had Claude been trying to get his attention? “Yes?”

Claude gave him a curious look before glancing to the others in the war room, and then back to him. “Are you feeling alright? You seem… out of sorts.”

Anger flared up inside Byleth, though he fought to keep it down, trying to quell his inner thoughts of _'of course I’m not alright, we’ve explained the plan three times and still some of these imbeciles don’t get it'_. He winced at the scathing diatribe, knowing he was normally patient; he certainly didn’t believe any of his former students were imbeciles.

“Byleth.”

Again, Claude had to call for his attention. This was beyond embarrassing. What was wrong with him?

“I’m sorry, I- no, I’m not feeling very well at all. I don’t know what’s wrong…” he admitted, rubbing his left temple.

“Go then. If there’s anything you need to know I can catch you up later.” Claude smiled at him, though there was concern evident on his face as well.

Fighting hard to keep his voice even, Byleth stood and nodded. “I appreciate it.” It felt like a lie. He knew, deep down, underneath this strange aggressiveness he’d suddenly developed, that he did appreciate it, but all those worried faces watching him as he left the room made his blood boil. He had to fight hard to keep his expression neutral, to hide the frustration he was experiencing.

He headed straight to his room, hoping that with a little sleep he could shake this mysterious condition, but slumber seemed far out of reach. He was too restless, too caught up in worrying about what might be wrong with him while his emotions continued to churn.

About an hour after he left the meeting, there was a knock on his door; he’d been in the middle of trying to nod off again, and it startled him. “Who’s there?!” he roared ferociously before realizing his error and sprinting to the door to open it, apologizing profusely. It was Claude, looking understandably startled. He had come to let Byleth know that nothing else important happened at the meeting, and that everyone was concerned about him and wanted to give him their well wishes. Byleth nodded, fighting to control his strange, new temperament. “I appreciate it Claude. I think that perhaps I just need to sleep whatever this is off…” he said sheepishly.

“Come on, Teach. You should go see Professor Manuela. Or at least one of the healers… Linhardt, or Marianne…” Claude suggested.

“No, no… I really don’t think that’s a good idea,” Byleth replied, shaking his head emphatically.

Claude made a small noise of disappointment, shaking his head slowly, until he paused abruptly, a coy grin blooming on his face. “It’s alright… I’ll just let Yuri know you’re not feeling well. I’m sure he’ll be able to convince you to see Manuela…”

Byleth felt his face heat up, and he had to grip the doorknob tightly to stop himself from lashing out at Claude. “Please… don’t. Please,” he implored, trying to keep his voice even. “I need to go back inside now. Thank you for checking on me.” Before Claude could respond, Byleth had turned and retreated, locking the door behind him.

Yuri coming here would be a disaster. Something inside him, some almost _bestial_ urge stirred at the idea of getting angry at him; perhaps he would pick the lock on the door even after Byleth asked him to leave. In his mind he pushed Yuri up against the wall, both of them breathing heavily… Byleth felt himself blush again at the images in his head, but they really were more worrying than embarrassing. The last thing he wanted to do was hurt Yuri. But if he came here… Byleth couldn’t imagine him going away no matter how much he insisted, and he was all too aware that a locked door wouldn’t keep his nimble-fingered lover out of his room.

Whatever was wrong with him, it needed to stop, and soon. He almost considered going to Manuela, or even sending her an owl asking her to come to him, but he didn’t want to hurt _anyone_ , and there was no guarantee she would even be able to help him.

In the process of trying to find something to focus his mind on, Byleth’s eyes passed over the bottle of mead he had been drinking last night. It had been a gift from one of the vendors in the marketplace, who thanked him for trying to bring stability to Fodlan, allowing traders and merchants to continue making a living. Though now that he really thought about it, he didn’t actually recognize the man who had given him the mead. Byleth had thought that perhaps he was a merchant who passed through the monastery infrequently, but what if he wasn’t what he claimed at all, and he had other agendas involving delivering the bottle of mead to Byleth? He picked up the half-empty bottle, staring at its contents through the dark glass, then gave himself a mental shake and put the bottle back down. Whatever was wrong with him must be making him paranoid, not just angry. Why would anyone want to poison him? He almost kicked the bottle, but he resisted the urge and instead flopped himself particularly aggressively onto his bed.

A couple hours passed and Byleth was feeling increasingly restless and upset, unable to calm himself or concentrate on reading, writing, training, polishing his armour… nothing seemed to distract him from the violent urges gnawing at him. Worse yet, now his thoughts occasionally shifted to Yuri, to images of himself, pinning Yuri down, biting his neck as he fucked him _hard_ ; he found it disturbingly tough to wrench his mind from those sorts of scenarios. Some part of him actually wanted Yuri to come to his room, breaking in after being told to go away, just so he could… mark him. Lay claim, dominate…

I’m going mad, aren’t I? Is this some sort of punishment for being a vessel for the Goddess? Those depraved thoughts were distressingly tantalizing. It was like this odd aggression was becoming a part of him, blending into his own sense of self, and fighting it felt like denying his own existence. Some part of his mind acknowledged how base, how _animalistic_ this strange temperament seemed, and it frightened the still-lucid part of him. What was happening to him?

Byleth was starting to lose track of the passage of time when he heard footsteps, followed by a knock on his door. He didn’t want to answer it, so he stared at it from where he was huddled on his bed, frowning as he considered his options. The knock came again, and Byleth very suddenly became aware of a new phenomenon. A scent. Whoever was standing outside the door smelled distinctly of musk with a sharp tinge of iron, like they had toiled long and hard throughout the day, but there was an underlying note of… vanilla? It was distinctly sweet. The iron scent seemed familiar, but it took Byleth a moment to place it – Abyss. With all the water down there, and the way the air could settle for days and grow stale, the place often carried the scent of wet brick and metal

“Byleth? You alright?”

Hearing the voice confirmed what Byleth had already suspected, and he fought hard to keep his feverish desire in check. “Yuri? I’m fine. But it’s not safe… No one should be around me. It’s not safe,” he called back, knowing his voice sounded strained, which was only going to worry him more.

“Pretty sure I’ve said something similar to you before and you kept insisting anyway. So let me in.”

“No, this isn’t the same. I don’t know what I’ll do. I- I can’t control myself.” Saying that out loud forced Byleth to really acknowledge what was going on, and suddenly he was frightened, beginning to shake as he mentally thought through the situation, trying to find a way out while still keeping himself together.

“Right, well, I don’t really know what you mean, but I’m coming in, so you can explain.” Byleth opened his mouth to protest, but he could already hear Yuri picking the lock.

Wait, since when have I been able to hear that? The tumbler shouldn’t be that loud…

It was only seconds before Yuri was opening his door, stepping in only to freeze upon seeing Byleth. Slowly he closed the door, looking alarmed. “Have you… looked in a mirror recently?”

Yuri’s voice was like velvet, and while ordinarily that was obvious to him, now it was… more pronounced. Like he could feel each and every luxuriant fibre caress his skin, as if those fibres were the syllables he uttered. It didn’t really make sense to him, but he knew that he was going to have a lot of trouble talking himself out of taking all of his frustration from the last six hours out on Yuri. And now he had to wonder if his appearance had somehow changed.

“No… I… haven’t,” he replied carefully, his unblinking gaze fixed on Yuri. For a brief moment, something like discomfort passed over Yuri’s face, until he covered it up with a mask of neutrality. But Byleth saw it, becoming hyper-aware and extremely self-conscious of just how intensely he was staring, though he couldn’t look away… and wasn’t sure he even wanted to. Despite the simple clothes Yuri was wearing, he seemed like a work of art, crafted from the finest materials the world had to offer. 

What is happening? Why am I so… Byleth realized at that moment that his senses all seemed to be strangely enhanced. That was why he had been able to distinctly smell Yuri on the other side of the door, why he could hear the tumbler in the doorknob, and why was currently hearing and seeing Yuri like he never had before. Isolated in his room for the last few hours, trying to distract himself, he didn’t notice the changes as they happened. Briefly he wondered if his senses of taste and touch were also enhanced… though he really had no intention of experimenting to find out, with the potential for danger.

Yuri’s voice broke through his thoughts. “You… probably should… I don’t think I could explain.” He also stepped back slightly, and Byleth had the distinct feeling that Yuri realized now that there might have been a good reason for Byleth to tell him not to come in.

Byleth had a small mirror in his desk, so he got off his bed, finally tearing his eyes away from Yuri, and opened the drawer to retrieve it.

Somehow, over the last few hours, without him even realizing it, Byleth’s skin had developed what seemed like patches of dark scales, one of which started on his neck and ran along his jaw, almost up to his ear, while another peaked out from under his hair on the opposite side of his face. His pupils had nearly completely dilated, and his irises were a much brighter green than normal… most bizarrely was how the whites of his eyes had darkened, nearly black. Now that he was more focussed on the changes, he noticed that his teeth and nails seemed to be slightly sharper, and his fingernails at least had taken on a dark hue similar to the patches of scale. Other parts of his body seemed changed as well. His pulse was faster, though he still lacked a heartbeat, and his muscles felt… stronger, somehow, and ready… they twitched as if anticipating a fight, or perhaps a hunt.

He couldn’t fathom how any of this happened without him noticing.

His thoughts were interrupted when he became aware of Yuri moving closer to him, the combination of seeing and smelling him suddenly overwhelming Byleth. He backed away, quickly discarding the mirror on the desk. “No. Stay away. You have to leave. I don’t know what’s wrong with me but I’m not letting whatever this is affect you too.” A strange, primal urge had him inhaling deeply as Yuri approached, and for a moment the world, and the remnants of his rational thoughts, both became out of reach, blurred; he realized he could easily get drunk on that wonderful scent, let go and simply fall into oblivion. Just as quickly though, he returned to himself, lucidity snapping back in place.

Yuri raised an eyebrow. “Do you think it’s contagious? Claude seemed to think you were sick…”

Byleth sighed in irritation at the mention of Claude, wishing he hadn’t gone and told Yuri that he was sick. It… didn’t really seem that way anymore, did it? This wasn’t some sort of illness...

“I don’t know, but I don’t want to find out either.”

Yuri crossed his arms, eyeing Byleth carefully. Byleth stared back, feeling like he was just barely keeping himself from lunging at Yuri. He felt his muscles twitch as he held himself back, and with a twinge of discomfort, he realized he was beginning to grow aroused, Yuri’s scent slowly making his blood boil.

“At least let me look you over, yeah? I’m no Manuela but I _know_ you know that I’m good enough.” Yuri suggested, clearly not willing to take no for an answer.

Despite that, Byleth was still going to try. “No… if you come any closer… I don’t know what will happen…” That was a blatant lie. He knew exactly what would happen, and it made the still-sane part of his mind squirm in discomfort. With how strong he was now, Byleth didn’t see how there was any way Yuri could stop him.

“I’m sure if I come close enough to use some magic, I’m not going to catch whatever this is, if it’s even contagious or an illness.” Yuri reasoned. “Though, I don’t think it is.”

Byleth found he couldn’t really refute Yuri’s logic; between the two of them, he would know better. Perhaps it was better to just admit to what the problem was. “I’m… afraid I’m going to attack you,” he explained hesitantly.

That seemed to give Yuri pause, though he didn’t seem convinced. “And why’s that?”

Oh boy. That was the part Byleth didn’t want to explain. “Whatever this is… it seems to be making me… very aggressive. I’m… _Goddess_ , I’m,” Byleth started, but Yuri moved closer, and his scent with him, causing Byleth to very nearly grab him. 

Yuri froze partway to Byleth, looking alarmed. “Something about your eyes is… unsettling. The way you keep looking at me…" He trailed off, closing his eyes briefly before he looked back up. Byleth hoped Yuri was starting to understand how much danger he was in. “Please just tell me what’s going on. I want to help you but I can’t if you won’t tell me anything," Yuri pleaded. His voice was unsteady, and Byleth realized that he was actually more upset that he was letting on.

“I- I don’t want to hurt you,” was all that came out as Byleth gritted his teeth, gripping the shelf behind him so hard that his nails were digging into it. “But… whatever this is… this… _condition_ it… it's driving me mad… with need. For you.” he finally admitted, ripping his gaze away. The words came out almost strangled, he was trying so hard to deny what was happening to him.

"...what?”

Byleth let out a noise of frustration, something between a loud exhale and a growl, and shifted, his muscles tensing painfully after so much anticipation. “I wondered… if that mead… if there was something in it… but that seemed paranoid.” He gestured stiffly to the dark bottle on the ground behind his bed, and Yuri moved to pick it up, the shifting of his scent in the air causing Byleth to let out another strangled noise.

“Does it hurt?” Yuri asked, alarmed. He picked up the bottle and gave it a quick look over, but his concerned gaze settled on Byleth.

“Not really. Just… uncomfortable. Tense muscles… from struggling against... urges…" Byleth tried to explain, until an intense shudder ran down his spine.

Yuri nodded, seeming to understand what Byleth was trying to say. “Yeah, okay,” he acknowledged, uncorking the bottle. He looked around for a moment, until he spotted Byleth’s tea set, reaching out to grab a teacup which he then placed on the desk. He poured some of the amber liquid into the cup, and then recorked the bottle, setting it aside before leaning in to examine the mead. He didn’t seem to find anything wrong with it initially, at least as far as Byleth could tell, but then he started examining it with some sort of faith spell, looking agitated after only a few moments. “There’s definitely something in here that’s not supposed to be in here. I can’t tell what it is, but it’s magical and… it feels dark. I’ve seen magic like this before, but I can’t seem to recall what it was, or where…”

Byleth made a noise of frustration that had Yuri glancing at him again with concern. "Well, I won't be accepting random gifts from strangers now for a very long time, if ever again… I really didn't need this right now." He shuddered, breathing heavily.

“If I’m understanding what you’re saying, you’re… having urges,” Yuri started, pausing for a moment as he shifted his weight and glanced away, seeming uncomfortable. Byleth sensed a change in the air; Yuri’s scent had shifted slightly, and now that musk felt heavy, making his thoughts foggier than they already were. He felt his arousal surge, and he snarled as he continued to hold himself back, his nails now digging into the shelf painfully. Yuri seemed to him less alarmed and more concerned now, and he moved closer, even as Byleth began to shake his head furiously.

“No, no, please don’t come over here. I don’t know if I’ll be able to stop myself,” he ground out, squeezing his eyes shut and turning away. It didn’t matter that he couldn’t see Yuri, though, because he could still smell him, feel him getting closer, _too close_. 

Then there was something cold and sharp pressed against his neck.

His eyes snapped open, and he realized that Yuri had pulled a dagger from somewhere and was pressing it against his neck, almost enough pressure on the blade to draw blood. “I’ll stab you if I need to, so don’t worry about it,” he said, and though Byleth could feel the blood coursing through his veins like fire, the threat seemed to put a bit of a damper on his viciousness. He nodded, closing his eyes and trying to concentrate on breathing as he felt the warm light of Yuri’s magic against his skin. Unfortunately that meant that he was flooding his senses with Yuri’s scent, which was far from relaxing with how tight his pants were now. “I think once the… drug, I suppose, leaves your system, you should mostly go back to normal,” Yuri explained. “I think it would be better if Manuela or at the very least Linhardt or Marianne could verify that, though. I’m not 100 percent- wait.” He paused, and Byleth opened his eyes again to see Yuri looking perplexed. “This magic… It's similar to the magic in those corrupted crest stones that cause demonic beasts to transform. That’s why I thought it felt familiar.”

Byleth grimaced, tensing up even more than he was already. “Alright then… just… leave me here. Eventually it will work itself out of my system, and I’ll be fine,” he suggested, wincing as he opened his eyes and saw the look of determination on Yuri’s face.

“No. You’re going to drive yourself mad in here alone. And…” Yuri answered, pausing, “I think you’ll find that some… physical activity… might help work it out faster…” With the dagger still pressed to his throat, Yuri moved closer, pressing his body against Byleth’s. He was unmistakably aroused, and Byleth growled, his already tenuous control slipping further. He was sure the only thing keeping him back was that dagger.

At least it was, until Yuri placed it on the shelf and leaned in to kiss him.

Within an instant, Byleth had thrown Yuri to the floor, pinning him down with his body and grinding against him. He moaned, the friction blissful but still not enough. He leaned in to bite Yuri’s neck, just barely hard enough to draw blood, which he immediately licked up. Combined, the taste and scent of Yuri almost made him high, but the world came rushing back as a sharp blade brushed against his neck. He shouldn't have been surprised that Yuri had another dagger hidden somewhere; after all, he wouldn't want to claim someone who couldn't keep up with him. Yuri was exquisitely skilled, and his demonstration of those skills would have turned Byleth on more if it had been possible.

"Really? Biting?" Yuri scowled as he pressed the blade against Byleth's neck, drawing a thin line of blood. "If you really need to mark me up, at least keep it somewhere no one will see. _Under_ clothes, you know?"

Byleth stared for a moment, wincing at the sharp pain in his neck, but then he nodded carefully. He was torn, because he wanted to respect his mate's wishes, but he also wanted to make sure others knew he was claimed. There were other, more subtle ways to accomplish that, though. 

Apparently satisfied with the answer, Yuri withdrew the blade, carefully depositing it on the floor nearby, underneath the desk. Byleth huffed, leaning down to nip at Yuri's ear in defiance, before shifting to roughly claim his lips.

\---------- ---------- ----------

Yuri was rarely the sort of person who didn't heed his own mind when it was in full opposition to something, but he was so mindlessly aroused by the idea of Byleth fucking him into oblivion that, in spite of the terror he was experiencing (or possibly because of it), he'd decided that, _yes_ , he did indeed want to give into whatever bestial instincts were being amplified in Byleth. Being so swiftly tossed to the floor and bitten had him second guessing himself, but thankfully he had a second dagger tucked away in his boot, and he was able to put it to good use.

Being so swiftly tossed to the floor and bitten also had him growing painfully hard. With Byleth straddling him like this, he was able to buck up a bit, but it wasn't nearly enough. Still, he moaned against Byleth's lips, hoping he would take the hint. He couldn’t exactly do much himself, with how thoroughly he was being devoured. It occurred to him to try to remove his clothes, since in this state Byleth was potentially just going to rip them off of him if given the chance. He reached between them to undo the ties on the front of his pants; Byleth noticed and shifted back, seemingly to give him space. He stopped kissing him, and instead grabbed his hair and wrenched his head to the side. Yuri yelped loudly, which seemed to give Byleth pause, but it was only for a moment before he leaned down to lick at the wound on his neck.

Anticipation made his fingers unsteady, but eventually Yuri had his pants undone. Before he could shuck them off himself, Byleth was moving to push his hands away, quickly pulling them off of him, along with his smallclothes and boots. Byleth paused, not even to bother hiding how intensely he was staring at Yuri’s body before he stood, quickly removing his own tunic. Yuri watched with bated breath as more scales were revealed, various patches on his shoulders and sides, but most prominently on his chest, particularly on the left side where, presumably, his heart was. If Yuri’s mind hadn’t been so heavily fogged with arousal, he might have taken the time to mull over this strange feature of his lover, one of many, but his eyes caught sight of the dark scales on Byleth’s lower stomach, and any intellectual thought became smoke in his smouldering desire. Those scales were less patchy and trailed down low, disappearing under his pants, and Yuri’s mouth dried as he wondered what other unseen changes were in store for him.

Strong arms lifted him off the floor, and the power Yuri could feel thrumming in those muscles made his head swim. Byleth tossed him onto the bed and crawled up after him, pushing his legs up and apart to settle between them. Yuri tried to raise his hand to touch Byleth’s cheek, trepidation causing him to pause part way when he realized how much his hand was shaking. Byleth seemed to sense what he was trying to do though, and he closed the gap, leaning his face towards Yuri’s hand and nuzzling up to it. That calmed him a bit, until Byleth flicked Yuri’s thumb with his tongue; he barely caught sight of it, but it was darker than it should have been and seemed to be unusually long and thin. His heart hammered in his chest. It was strange how arousing fear could be. At this point, he was so far gone he could barely tell where his fear ended and his desire began.

Byleth licked his hand a bit more before pushing it away, shifting to lean in closer. He grabbed Yuri’s legs, under the knee, pushing as he leaned in so Yuri was nearly folded in half at the hips. Byleth’s scales against his skin was an unexpected but not entirely unpleasant feeling, and at first he hissed at the contact, particularly where the stomach scales brushed against his taut balls. 

Yuri didn’t hesitate to tilt his head up to meet Byleth’s mouth as he descended, running his hands up Byleth’s back and into his hair. He moaned, his lips parting, and felt Byleth slip that strange tongue into his mouth. Despite seeing it moments before, albeit briefly, Yuri was still surprised at how… long it was. He shivered as Byleth effortlessly pinned down his tongue with his own, melting with how thoroughly Byleth was consuming him. 

When Byleth finally pulled away Yuri was practically gasping for air and feeling light-headed. Byleth seemed to take notice; he paused, giving Yuri a questioning look before leaning back in to nuzzle his cheek.

“Thanks…” Yuri muttered weakly, running his fingers through Byleth’s hair. He made a sound almost like a purr, and for a moment Yuri was sure his heart was going to beat right out of his chest. Once he had recovered, Byleth pulled away, being considerably more gentle. He kissed his way down Yuri’s neck, nipping at the dip in his throat, but he seemed to have forgotten that Yuri was still wearing his shirt. He made a low noise of frustration when his mouth met fabric, and it seemed for a moment that he was going to simply rip the shirt off. 

“Wait,” Yuri requested firmly, trying to bat Byleth’s hands away. Byleth grumbled as he pulled away, frowning, his eyes flashing in irritation, and it sounded very much like he wasn’t going to wait long. As it was, Yuri didn’t particularly want to wait either, but he certainly preferred to keep his clothes from getting destroyed. He quickly pulled the shirt up and over his head, tossing it over the side of the bed. Predictably, Byleth’s mouth was back on him almost instantly, licking at his collarbones. Yuri ran a hand up his back, tangling his fingers in Byleth’s hair again, trying to encourage him. 

It didn’t take long for Byleth to add more fresh bites to Yuri’s chest, though to his credit he did restrict himself to biting only where they would be easy to hide. Yuri found himself growing frustrated as Byleth marked him up, his orgasm still out of reach even with how aroused he was. He rocked his hips impatiently, but Byleth just tightened his grip on Yuri’s legs in an attempt to stop him from moving. 

“Please…” he moaned, his voice whinier and shakier than he would have liked. It was embarrassing but it caught Byleth’s attention, and he looked up, shifting his mouth to Yuri’s thigh. He bit down gently, causing Yuri to moan again, still shamefully whiny. “Please…” He rocked his hips again to try to get his point across, and Byleth smiled as he licked a path down Yuri’s thigh. 

Unfortunately for Yuri, it seemed he wasn’t done teasing yet. Byleth barely let his tongue graze Yuri’s cock before he was heading lower, and Yuri let out a string of gasps and moans as Byleth prodded and licked at the sensitive path of skin behind his balls, occasionally letting his tongue stray to the tight hole below.

"By… I need… Please," Yuri groaned, shifting his hips in an attempt to get that delectable tongue to trail lower. He was going to beg more when he felt a more purposeful prod at his entrance, and with a long, shuddering moan he rolled his hips up more to encourage Byleth further. It didn't take long for the tip of his tongue to slip inside, and Yuri hissed, shifting around to try to get more, but now Byleth pressed more firmly on his thighs to hold him in place. 

Despite stopping him, it did seem like Byleth was done teasing; he apparently just wanted to fuck Yuri on his own terms, at his own pace. Yuri could feel his hands on his ass, spreading him open as he slowly fucked him with his tongue, and occasionally sharp nails or teeth would skim the surface of his skin, hard enough to add some bite but not hard enough to make him bleed. Good… even in this strange form, Byleth was still being careful enough. He should have given himself more credit.

Yuri found himself clutching at the sheets as he was thoroughly eaten out, his voice growing shamefully whiny again as he drew close to orgasm but still not close enough. He tried to protest a couple of times, but Byleth would just dig his claws into the supple flesh in his grasp, still thankfully not hard enough to pierce, but definitely close enough that Yuri decided it wasn’t worth it. He was sure Byleth would get him there eventually, so for now it was good enough to just let himself enjoy it.

Finally, after it seemed he’d been writhing around on the bed for several minutes, a near-constant stream of shaky, lewd moans pouring from his mouth, Byleth pulled away, licking a path up his balls and cock. “Yesssss,” Yuri hissed, but then the contact was gone. He raised his head, and saw that Byleth had stood and was watching him, licking his lips as he undid the front of his pants, and for a moment Yuri was sure he would come just from that image. That notion was quickly challenged as Byleth’s pants fell, revealing more scales that seemed to cover most of his groin area, except his cock, which was still much thicker and darker than normal. 

“Let me-” Yuri started, trying to sit up. Byleth pushed him back down as he climbed back onto the bed, still staring at him. Yuri’s eyes flitted between that swollen cock and Byleth’s face as he tried to reach out. “Come closer. I want to… see…”

Byleth seemed to understand, and he shifted until he was straddling Yuri’s chest. Yuri was sure he stopped breathing as Byleth came closer, letting his eyes fall closed as he touched his strange cock. There were thin scales at the base, though thicker ones trailed down between his legs, covering his balls, which were tucked close to his body instead of hanging loose. The shaft was thick and ridged on the underside, smooth on the top, with the last ridge being about where the head would have started, with no discernable difference between the head and shaft otherwise. The foreskin retracted behind the underside ridge, although upon further handling he realized that this… foreridge, he decided to call it, seemed to be partially composed of a gland that secreted some sort of slick fluid, which explained why the head felt wet. He’d initially thought it was precum, but this fluid seemed more likely. 

He also noticed that when he touched the gland, Byleth moaned, practically shuddering with it. He was watching Yuri carefully, his face completely flushed, and this time Yuri watched him back as he ran his fingers across the gland again. When he got the exact same reaction, he decided to take it up a notch, taking his cock in hand and rubbing it up and down, just as he might his own. Byleth flung his head back, letting out a loud, rapturous moan, and his whole body spasmed. His shaking increased in intensity as Yuri kept up the pace, and eventually he noticed that as the slick substance built up on his hand, he was spreading it up and down the entire length, and he realized it was some sort of natural lubricant. It wasn’t long before Byleth reached out to still his hand, grabbing it, and as he backed away, he very pointedly placed Yuri’s hand, palm down, between his legs, and then brushed against his ass with the back of his hand.

Oh. That did make sense, didn’t it. Yuri assumed he would have to go get the oil at some point soon, but his hand was already coated in Byleth’s natural slickness, so he shifted his hips up and brushed his fingers against his hole, slipping two in to get himself better prepared. Normally he didn’t really need too much stretching, but Byleth’s cock was much thicker and decidedly longer as well, so it seemed wise.

Byleth’s eyes were unabashedly locked on Yuri’s fingers as he sunk them inside himself and retracted them, over and over as he tried to open himself up as much as possible. It was obvious from the way Byleth’s eyebrow began to twitch that he was growing impatient, so with a smirk, Yuri decided to continue being a tease. He moaned loudly, very much for show as he slowly circled his rim and then pushed past, gripping the sheets with his other hand. Byleth growled in warning, his eyes flashing, and suddenly Yuri found himself on his stomach, bracing himself on his free arm as Byleth gripped the other. With a huff, Byleth let go of his arm and moved to straddle his thighs. Yuri moaned with anticipation, his fists balled in the sheets again.

It seemed for a moment like Byleth was going to tease him in return when Yuri felt his slick cock slide down the cleft of his ass, only to have him thrust between his cheeks a few times. He realized quickly that Byleth was trying to get more slick on him, but that didn’t stop his breathing from picking up as he felt his blood rush, his heart hammering in his chest. He almost whined when he finally felt the tip at his entrance, and then Byleth was pushing inside him. He made a strangled noise somewhere between a moan and a cry as he felt his hole stretch to accommodate the intrusion. He could hear Byleth behind him making soft noises as he slipped further inside, and he rolled his hips, groaning, as a sudden desire to be stuffed full hit him. He moaned loudly as the first ridge slipped inside him, rolling his hips again to get more.

Suddenly Byleth was holding him down completely, pushing in with much more vigour, and Yuri realized that he’d been holding back, probably concerned about hurting him. Each ridge made him cry out, and once the whole length was sheathed inside him, Byleth sunk all the way down on top of Yuri, covering his entire body with his own. Yuri felt Byleth’s tongue on the shell of his ear, and he tried to turn his head, hoping for a kiss, until he felt fingers in his hair, yanking his head back around. Byleth’s other hand slipped under his throat, and for a brief moment a bit of his earlier fear slipped back in, until suddenly Byleth was withdrawing, thrusting back in just as abruptly.

Byleth was taking an unusual amount of interest in his hair; he seemed to have buried his face in it, almost nuzzling the back of his head, a strange noise between a growl and a moan coming from his throat. Even with his mind’s distractions, he realized, albeit slowly, that Byleth was smelling him. 

It didn’t take long for Yuri to come, with the full, fast strokes Byleth’s hips were slamming out. His mouth opened in a near-silent scream as he spasmed, his cock twitching underneath him as his balls tightened and he spilled onto what little space there was between his body and the sheets. His chest heaving and his mind foggy, he only barely registered that Byleth had stopped moving, his cock fully inside him. He let his eyes slipped close, though he realized that Byleth hadn’t come yet… he must be close, right? He would either come soon, or withdraw and stroke himself off over Yuri. 

Except, this wasn’t exactly happening under normal circumstances, was it? He heard Byleth growl quietly, the sound close to his ear, and then he slowly began to thrust again. It wasn’t quite the pace from moments earlier, but if the noises Byleth was making were any indication, this was far from over.

Between his sensitive, flaccid cock rubbing against the sheets under him and Byleth’s ridges rubbing at his prostate, it wasn’t long before Yuri was crying out in protest. As Byleth’s pace picked up, his hips snapping faster than they had even before Yuri had come, the overstimulation became too much; he could feel himself shuddering with it now, but with Byleth completely on top of him and in this condition, there was no way to get him to stop. Tears pricked at the corners of his eyes, and he whined pathetically as Byleth slammed into him, gripping the sheets as his whole body shook with pleasure. 

After a few minutes, Yuri was half-hard again, every thrust nearly agonizing at this point. Despite how overstimulated he was, he could feel a certain pressure building up within him, until Byleth’s cock hit that sweet spot just _right_ , breaking that pressure and causing his body to seize as he came. A long moan spilled from his lips, and as he slid down from that high he could already feel the pleasure mounting inside himself again. With the excessive stimulation his prostate was getting, he knew it wouldn’t be long before the sheets beneath him were embarrassingly wet.

He didn’t understand how Byleth was still going, but he guessed that once his orgasm came, it was probably going to be long and explosive. The noises he was making were changing, sounding less like growls and more like moans, but were also growing louder. Yuri was starting to feel like he was going to be bruised for weeks if his hips didn’t just break first. His own cries and moans were growing more intense as the seconds and minutes passed, and he was growing so overwhelmed with the burn of it all that he was sure he would be sobbing soon.

Finally, Byleth curled around him a bit, pulling his legs underneath himself as he grabbed Yuri’s hips, slamming into him harder than ever. He bit down on Yuri’s shoulder none-too-gently, keening loudly as his body went completely taut. Yuri cried out, both at the feeling of being bitten and of being filled up with an abundance of cum. Byleth spasmed several times, his thick, solid cock twitching inside Yuri as he continued to spill, and Yuri let out a loud, shuddering moan as he came again. Completely boneless, Yuri collapsed completely, Byleth sinking onto him limply seconds later, and Yuri let his eyes slip closed as unconsciousness claimed him.

\---------- ---------- ----------

Byleth felt extremely disoriented when he finally started to come out of the fog, his eyes slipping open. There was a pleasant smell very close to him, and at first all he could see was a blur of lavender. Once his eyes cleared, he realized his face was still buried in Yuri’s hair. It took him a moment to remember what had transpired, and he was alarmed to recall himself, still in that monstrous condition, fucking Yuri very hard into the bed. He rolled off of him and to the side, noting faintly that the bed was desperately in need of fresh sheets… and maybe even a fresh mattress, he realized with a grimace. He still had his oddly sharp teeth and nails - and, he realized with a start, blood on his mouth, Yuri’s blood if he was interpreting the wound on his shoulder correctly. 

In a panic, he crossed his legs, pulling Yuri into his lap, trying to call on his faith magic to seal up several bites; it came, though it felt like it took more effort than usual. Yuri’s neck and shoulder wounds closed up with little effort otherwise. 

He felt tears forming in his eyes. How could he do this? He knew he wasn’t entirely in his right mind, but for most of the time he was actually surprised at how he was able to not entirely lose it, some of his logic retained, but with an animalistic shadow over it. Towards the end, as he got closer to his goal, his need growing, he lost most of his control, but that was no excuse…

A groan cut through his inner monologue, and he looked down to see Yuri’s eyes flutter open. He looked just as disoriented as Byleth had felt when he awoke, and he gave Yuri a few minutes to gather himself. He grabbed a pillow from behind himself, using it to prop Yuri up a bit better, and then slipped his fingers into the short hairs at the nape of his neck to comfort him, slowly caressing the spot.

“Hey…” Byleth greeted quietly, trying to smile though he felt awful, both from the danger he’d put Yuri in and the damage the drug had done to him. It suddenly occurred to him that, though his transformation seemed to have stayed in effect, his temperament had returned to normal.

Yuri smiled up at him, but his eyes slipped closed again; he looked exhausted. He did curl up a bit, shifting more onto his side and closer to Byleth. “Hey…” he mumbled after a moment, still smiling a bit. “Thanks for healing me…”

A tear slipped over his eyelid and down his cheek. He was so ashamed, he couldn’t even accept Yuri’s thanks. But then Yuri was sitting up, his arms wrapped around Byleth’s shoulders. “Hey. None of that. You might have pounded me into the bed pretty thoroughly, but you certainly didn’t drug yourself.”

“Yuri… I-”

“Besides, getting pounded into the bed was pretty fun. Maybe you had more stamina than I did, but if I could do it again I certainly would,” Yuri continued, flashing Byleth a tired grin. “Definitely not right now though.”

Byleth couldn’t help the smile that bloomed on his face. Leave it to Yuri to make light of how seriously Byleth could have hurt him. “Of course.”

Apparently satisfied that Byleth was done blaming himself, Yuri leaned his head on Byleth’s shoulder, his eyes slipping closed again. Byleth took the pillow and put it back behind himself with the others, and then leaned back slowly, trying to find a way for them to lay down while avoiding the mess they had made. Though, when Yuri had sat up in his lap, quite a bit of cum had dribbled out of him, so that was looking difficult. Still, he did the best he could, knowing they couldn’t rest for too long or the bed would become unsalvageable.

After they rested, they decided incineration was the best fate for the bed linens, neither of them particularly enthused by the idea of trying to sneak them to the monastery laundry only to have awkward questions asked. Byleth already had to sneak around in a cloak to retrieve a basin and the necessary water and soap for them to bathe, since if Yuri moved he would just make more of a mess. Instead he sat in the rolled up bundle of sheets on the floor, like it was a nest, blushing furiously as cum leaked from his ass. Byleth felt terrible about the whole situation, but there wasn’t much to be done about it now.

“How do you feel?” Byleth asked, dropping a kiss on the top of Yuri’s head. They were in the tub, relaxing in the hot water as Yuri sat in Byleth’s lap, leaning comfortably against him. Byleth still hadn’t changed back despite it having been almost 24 hours since he drank the mead, but Yuri said that because the change had been caused by magic, it might take magic to change him back.

“Much better. You?” Yuri turned slightly to look at him, still looking tired but otherwise much more like his usual self.

“Fine, I’m… just nervous, that’s all,” Byleth answered, looking at the patch of scales on his arm.

Yuri pursed his lips. “Let me try something,” he suggested, getting to his knees as he turned around fully.

Byleth shook his head, frowning a bit.. “Don’t waste your energy.”

“It’s not a waste of energy,” Yuri shot back, also wearing a frown. Byleth sighed.

“Alright… but if it’s not working just… don’t worry about it. You can try again tomorrow. Or I can go to Manuela. I should tell Seteth about the mead anyway…” Byleth reasoned. 

Yuri sighed. “I don’t think you’d want to go see either of them like this, yeah?" He smiled then, closing his eyes as he concentrated, placing his hand in the middle of Byleth’s chest. Byleth felt the warmth of his magic before he saw the telltale glow, and he wanted to sink into it, eyes slipping shut as he felt his muscles go slack. It quickly became apparent to him that this wasn’t a normal recover spell; the water began to glow as well, vivid even through Byleth's eyelids. The intensity of the light built dramatically, leaving Byleth glad that he had already closed his eyes. He was taken aback by the power of the spell, by how he could feel it gathering in the air and water around him. Concern struck him though as he considered how much energy Yuri must be using to cast this spell, hoping desperately that Yuri wasn’t hurting himself. The magic in the air began to gather slowly on his skin, like tiny crackles of static, until he almost felt like he was being struck by a strangely painless bolting spell. He wanted to reach out for Yuri, but his body felt tight, and no matter how hard he tried, he couldn’t even move a finger.

Suddenly the light faded, and Byleth opened his eyes; it had all collapsed in on the point at which Yuri was touching Byleth, where there was a single shining orb of energy. He felt an immense upwelling of emotion, radiating out from that point and throughout his body, until the orb faded and Yuri abruptly crumbled, falling against Byleth’s chest. 

“Yuri!” Byleth called, panicked. He carefully held him up, and his eyes slowly fluttered open, though he looked disoriented. 

“Did… did it work?” Yuri mumbled, blinking.

Byleth realized that a few things had changed; his teeth and nails seemed to be back to normal, and some of the scales had faded in colour or thinned, with a few disappearing altogether. “Somewhat,” he answered, watching Yuri’s face fall as he took in the few changes.

“Sorry. I guess my magic isn’t strong enough.” Yuri said, looking down at the water.

Byleth pulled him into a tight hug, stroking his back. “You tried though, and it did help. I appreciate it a lot."

Nodding, Yuri hugged Byleth back. He managed to pull a small smile. “I’m glad you’re happy, but I wish I could have done more.”

After they were washed and dried and the sheets had been disposed of, with new ones being procured, they settled into a nice, warm bed, clean linens and all. Yuri was still laughing at how long it had taken the sheets to catch on fire (courtesy Byleth's fire spell), and Byleth found it more and more amusing the longer Yuri laughed. Even so, they were both exhausted, and it took little time for them to fall asleep.

The next morning, Byleth awoke to fingers stroking his cheek. His eyes fluttered open, and he saw Yuri smiling at him. “It did work,” he said quietly.

Byleth was confused for a moment, until he realized that the cheek Yuri was stroking had still been scaly when they fell asleep last night. He took a mental inventory of the rest of his body, and realized that Yuri was right. 

“Even my eyes?” he asked, just to make sure.

Yuri nodded, his smile even brighter now. “Even your eyes.”

Byleth felt happiness swell in his chest, and he pulled Yuri close, hugging him as tightly as he could. Anything to show his appreciation to this wonderful man. He dropped a kiss on his head, and Yuri chuckled, letting himself be caught up in Byleth’s happiness. He positively glowed with it, and if anything, that made Byleth happier.

“Yuri… you’re amazing.”

For a moment Yuri was still, his eyes wide and his face a bit pinker than seconds ago, but then he broke into another small laugh, grinning. Byleth felt an upwelling of emotion in his chest, similar to the feeling he’d had the previous night in the bath. He’d thought then that it happened because of the magic, but now he wondered if the magic itself was the product of their shared emotions and mutual appreciation of each other. It was warm, and for a while the two of them just laid there, holding each other in the quiet glow of morning.

**Author's Note:**

> A few background notes that I wrote for myself as I was developing the idea:
> 
> (War Phase) Byleth is exposed, via a gifted bottle of mead, to a strange magical drug that the Agarthans are developing to cripple the Nabateans. They initially hadn’t intended on testing it on the Fell Star himself, but decided they were curious enough what effect it might have on him. Byleth awoke feeling strange the morning after he drank the bottle, and throughout the day he quickly lost control of the violent urges the drug was causing, confining himself to his room as a temporary solution.
> 
> Resolving to stay focused on his desire to not harm anyone, Byleth tries to distract himself with reading, with writing, even practicing stances, but nothing keeps him from nearly ripping his door off its hinges every time someone knocks on it. He knows he nearly scares a couple people, sending them away with a mix of frustration and anger, and he knows he’s just waiting for that one person who won’t take no for an answer. The one person who would likely be in the most danger around him right now. The one person he can’t seem to stop thinking about...
> 
> Byleth’s mindset becomes more and more neurotic as the drug sets in, his emotions a chaotic roil as the sane, intelligent part of him tries to fight against the instinctive urges that the drug is pulling to the surface. In a Nabatean, the drug is meant to reveal their draconic heritage and make them seem to be nothing more than beasts driven by instinct, and normally it wouldn’t affect a human at all. But with Sothis’ heart essentially replacing his own, Byleth’s body reacts strangely to the drug, causing him to exhibit a patchwork of draconic traits while slowly developing the characteristic animalistic behaviour, albeit at a much slower rate than a Nabatean would when exposed to the same dose. 
> 
> (Since food and shelter aren't a concern for Byleth, I figured that the bestial nature would cause him to go right to fucking and claiming a mate.)


End file.
